docs(modify-letter): Changed to the correct output

output section the first out put should be "John" instead of "Joe"

Co-authored-by: Pedro Ferreira <me.pedro.ferreira@gmail.com>

Author: ICEBergJQ

subjects/modify_letter/README.md

@@ -40,7 +40,7 @@ And its output
 
 ```console
 $ cargo run
-Joe is sleeping
+John is sleeping
 Jim is swimming
 bye byE
 $